Prominent bacterial heterotrophy and sources of 13C-depleted fatty acids to the interior Canada Basin

[摘要] In recent decades, the Canada Basin of the Arctic Ocean has experiencedrapidly decreasing summer sea ice coverage and freshening of surface waters.It is unclear how these changes translate to deeper waters, particularly asour baseline understanding of organic carbon cycling in the deep basin isquite limited. In this study, we describe full-depth profiles of theabundance, distribution and carbon isotopic composition of fatty acids fromsuspended particulate matter at a seasonally ice-free station and asemi-permanently ice-covered station. Fatty acids, along with suspendedparticulate organic carbon (POC), are more concentrated and ¹³C-enrichedunder ice cover than in ice-free waters. But this influence, apparent at50 m depth, does not propagate downward below 150 m depth, likely due tothe weak biological pump in the central Canada Basin. Branched fatty acidshave δ¹³C values that are similar to suspended POC at all depthsand are more ¹³C-enriched than even-numbered saturated fatty acids atdepths above 3000 m. These are likely to be produced in situ byheterotrophic bacteria incorporating organic carbon that is isotopicallysimilar to total suspended POC. Below surface waters, there is also thesuggestion of a source of saturated even-numbered fatty acids which couldrepresent contributions from laterally advected organic carbon and/or fromchemoautotrophic bacteria. At 3000 m depth and below, a greater relativeabundance of long-chain (C_20–24), branched and unsaturated fatty acidsis consistent with a stronger influence of re-suspended sedimentary organiccarbon. At these deep depths, two individual fatty acids (C₁₂ andiso-C₁₇) are significantly depleted in ¹³C, allowing for thepossibility that methane oxidizing bacteria contribute fatty acids, eitherdirectly to suspended particulate matter or to shallow sediments that aresubsequently mobilized and incorporated into suspended particulate matterwithin the deep basin.

[学科分类] 地球化学与岩石